Method of producing black oxide coated steel sheets



Patented Sept. 6, 1949 METHOD OFPRUDUCINGE BLALCKOXIDE COATED VSTEEL SHEETS .IolmiW."JIill,Mamsleld, Ohio; assigner, assignments,-,t0 Empire Steel Gmpany,afoot poration of- Delaware No Drawing. Application October 11, 1946,

Serial No. 702;'578- 14.Glltims (Cl. 14S-16.35)

This invention relates; asirrdicated', toa-method of producing coated" sheets', but':4 has-2 reference more.` particularly` to.l the. prodictiom. of' oxidecoated steel sheets;

Af primary object offthe invention'is :towproduce a-. steel sheet7 having an'. oxide'. coating, .which is extremely' attractive .f in'. appearance; andi which is'botl'r'a heat 4and 1corrosion1res1stant:

Another object of" the invention: is-l to provide an oxide-'coatedisteelsheet of the'fcl-iaracterfdee scribed whichr can: belbent; formed', drawn, or otherwise' fabricatedxwithout'breakage ofthe' oxa ide'filnr or coating.

A1furthenobject of the invention is'lto provide an oxideecoated'steel sheetoftliercharacter described Which `is especially'adaptedfr use inthe production of'v stoves, refrigerators; andi other household equipment, but which isadapted'v for other' uses:

Other objects and advantages' of-'the'invention will be apparent during the course of the follow ingadescription';

In.' accordance with' thetinvention; steelslieets are rst placed in an annealing box; andpild in such boxito'n; .desired height; the box'b'eingithen covered in" accordance With conventional pile' or boxV annealing?. practica.

The' pilesof :sheets Aisthenli'eatedto' an'- annealing: temperature 'Within'. the range of 'from 1 about SOOPFQ toxabout11200 E., the annealbeing con'- tinued until the sheets at the bottom ofI ther-pile attainrthessaidannealing temperature. In practice, the annealing period is from about 10 to about 20 hours; depending upon' the size and .number of4 sheets inthe pile. Duringithisfanneal,

a deoxdizing gas of any desiredfanalysisis passed through the annealingy box.

At the endlof f the aforesaid heating period, the heatingof the pile is discontinued, and bedorethe temperature of the pilefhas dropped belowakout 700? F., steam is introduced'into; the anneaiing box, causinga blue oxide coating-to be formed on both surfaces of each sheet,.andwhenltheftemperature of'the pile'has fallenloelovv aboutZ? F., th'ez'passageof steam into the fboxris discontinued.

The. cover of the box is: then"removed;I andthe sheets-.permitted to cool to atmospheric-temperatures. Y

The aforesaid treatment isthusa combination of a conventional anneal, andY a coating of the 'sheet surfaces with a lmor'co'ating of' afblue oxide, whichIZt'erm a steamblue oxide."

The sheets are thenremovedffiomitheannealing'. boor'` and are then` cold-rolledl to impart smoothness to the oxide-coated surfacesofthe sheets.

The cold-rolled sheets are then passed through a coating machine containing petroleum asphalt, which is a mixture of hydrocarbons and complex organic compounds derived from still residues 2 when; asphalt-base pertroleum'. is reiined.' For this particular' purpose the petroleumasphalttis preferably diluted?. with kerosene inf an: amount equal to one-third by volume of the'fcoating'fsolu# tion..

Theasheets; Whichfnavethusfbeen provided with a: coatings' of: petroleum. asphalt', are then run tlntougli'iaiycornveyors-type.'l furnace, in `which i they heated? to: ai temperature Within'. the range offrom about 500i E; t'oaboutrTOO. Fi, whichii's the ffiash :orf ignitionftemperature: of the: petroleum asphalt-kerosenecoating,l and! at;V this ytemperature',I .thezcoatin'g beeomesignited iandfburns with aeluminousyellow flame;v Ihe'fentirelcombustion otthecoating requires@ about'vthirty seconds and ati/the:conclsionzthereoiithe sheets arerun'out of'tiiefurnace-and'iontoasheetpiler' 'Iheeffectof the combustionbfthe'petroleum asphalt on petrol eum asphaltkeros ene `solution is toireduce :th'e'steam'blueoxidemte an iron-oxide ofi lower.' oxygen content; which is; jet;A black' in color: andi thel-physioaI appearanceaof which de'- pends on thernatureoff the original surface'v of the' steelsheet. If@ the-steelslieet hada smooth, mirrori-likenish, thelblaoirloxid'lof thenish'ed sheet' will be=highly" lustrous in' appearance; If the' steel sheet:h had a' roughenedi or' matte-like surface;- the bilaelr` oxide' will have a matte-like appearance.-

The r'lisiiedt product or" sheetis extremely attractive ini appearance' and ishigh'ly' resistant to'flieatas well'fasrborrosion. It eanbe'readily bentgr formed; drawn or otherwisefabricated, withoutbreakage off the' oxide nlm' or'coatin'g. By vir-tue* ofithese properties; itI is* admirably adapted forf' use inz. the pro ducticmy of stoves; re'- fri'gerators;1` andi other li'rmseliold'l equipment', but is well adapted for numerousotiier'applications or7 uses.;`

Insteadiofi-boxfor pile annealing the sheets;r as described, the sheets may be run through a' con'- tinuous" annealing furnace'4 andl heated to' the desired annealing' temperature, andf after the sheets have attained this temperature; stearnmay introducedinto'itlieefurnaceinorder to form theblue:oxide==coating tb=vvhicii reference has been' made;l

Moreover; the process `is=adaptedfoi-the "treatimentiofistiip'steelin a@ continuous manner.' The coi-lf of stripsteel may' either4A be' box-'annealed and? coatedfvvith the blue oxide; andI the strip th'enrun; in a continuous'v manner', through the coating' machine'L and coatingeburnin'g furnace, orfthe-sstrip may lielrun; in a continuousm'anner, througili-V a continuous; annealing furnace', in which' it'fisf annealed andl coated: with'- the blue oxide: and? then" run; in a" continuoust manner, through the coating machineandcoatingeldurnL ing furnace.

It will be understood that various changes in coating said sheets with petroleum asphalt, and.

4 10. A method, as definedinfclaim 9, in which lthe sheets are cold-rolled before being coated withY petroleum asphalt.

' .I 11. A method, as defined in claim 9, in which the iirst heating of the sheets is conducted in a A'deoxidizing atmosphere.

' 12. A method of producing heat and corrosion y resistant steel sheets, comprising the steps of piligniting said petroleum asphalt, whereby said coating burns and said blue oxide is reduced to a black oxide. n.

2. In a method of producing heat and Lcorrosion resistant steel sheets, the steps which consist in forming a blue oxide coating on said sheets,

coating said sheets with a solution of petroleum asphalt Vand kerosene, andthen igniting the asphalt and kerosene, whereby the asphalt and kerosene burn and said blue oxide is reduced to ablack oxide. Y

3. In a method of producing heat and corro'- sion resistant steel sheets, theY steps which consist in simultaneously annealing said sheets and forming a blue oxide coating thereon, coating said sheets with petroleum asphalt, and igniting said petroleum asphalt',`whereby said asphalt burns and said blue oxide is reduced toa black oxide.

4. In a method of producing heat andV corro.- sion resistant steel sheets, the steps which consist in simultaneously annealing said sheets and forming a blue oxide coating-thereon, coating said sheets with a mixture of petroleum asphalt and kerosene, and igniting the asphalt and kerosene, whereby the asphalt and kerosene burn ,and said blue oxide is reduced to a black oxide.

5. In a method of producing heat and 'corrosion resistant steel sheets-the steps which consist in heating said sheets, subjecting the heated `sheets to the action of steam, whereby a blue oxide Vwhereby-a blue oxide coating is formed on said sheets, coating said sheets with petroleum as,- phalt, and igniting said petroleum asphalt, whereby said asphalt burns and said blue oxide is converted to a black oxide. Y Y 5 '1. yA method, as dened in claim 6, inrwhich thesheets are heated. in'a deoxidizing atmosphere.

8. A method, as defined -in claim 6, in'iwhich the sheets are cold-rolled before being coated with petroleum asphalt.

9.- In a method of producing heat and corro-Y .sion resistant steel sheets, the steps whichconsist in heating said sheets to a temperature with]- in the range of from about 800 F. to about 1200 F., subjecting the sheets before they have cooled belowV about 700 F. to the action of steam, whereby a blue oxide-coating is formed on the sheets, coating said sheets with petroleum asphalt, and heating theA sheets to a temperature vat which said lastfnamed coating becomes ignited and burns with a luminous ame until it is consumed, the combustion of said petroleum asphalt coating converting said blue oxide coating to a coat.- ing which is black in color.

ing the sheets inan annealing box, covering said box, heating the pile to a temperature within the range o f from about 800 F. to about 1200 F.,

i passing a deoxidizing gas into said box during the heating period, discontinuing said heating, pass- .in color.

ing steam into the box before the temperature of the pile has been reduced below about 700 F., thereby forming a blueV oxide coating on'the sheets, cutting off the ilow of steam when the temperature of the-pilev has fallen to about 250 F., removing the cover from said box, permitting the sheets to cool to atmospheric temperature, removing thesheets from said box, cold-rolling the l.sheets to impartsmoothness to the coating,

Y coating the sheets Withfpetroleum asphalt,'pass sion resistant steel sheets, the steps Awhich consist ofapplyng t0 sheetshaving Ya blue oxide coating thereon a coating of petroleumV asphalt, and igniting said asphaltwhereby thefasphalt burns and said blue oxide is reduced toaI black oxide..

14. In a method of producing heat and corrosion resistant, steel sheets, the steps which consist of applying to sheets havinga blueoxide'coating thereon a coating of petroleum asphalt, and

heating the sheets to a temperature'oat which the asphalt coating becomes ignited and burns with a luminous flameuntil it is consumed, the combustion of said asphalt coating converting said blue oxide coating to a coating which is black Y AJOHN W. HILL. Y REFERENCES vCITED The following referencesA are of record in the file of this patent: f

Y VUNrrED sTA'rEsPATENTs Number Y OTHER REFERENCES Abraham, Asphalts and `Allied Substances, fth edition (1945), vol;Y I, page 463, Van Nostrand Co., Inc., New York.

H. Silman, Metal Industry, May 25, 1945, pages 330 to 332. f 

